1. Field of the Invention
The present invention relates to a vehicle engine output control method and a vehicle engine output control apparatus adopted when an engine output of a vehicle is controlled to a target engine output.
2. Description of the Related Art
A traction control apparatus is well known as one of control apparatus which control an engine output of a vehicle to a predetermined target torque. In the traction control apparatus, when an acceleration slip of the driving wheels is detected, a slip rate S is controlled to cause a coefficient .mu. of friction between the wheels and a road surface to fall within a maximum range (a hatched range in FIG. 18). The slip rate S is given by (VF-VB/VF).multidot.100 (%), where VF is the wheel velocity of driving wheels, and VB is the vehicle velocity. More specifically, when a slip of driving wheels is detected, an engine output is controlled to cause the slip rate S to fall within the hatched range, thereby controlling the coefficient .mu. of friction between wheels and a road surface to fall within the maximum range. Thus, an acceleration slip of driving wheels is prevented to improve acceleration characteristics of a vehicle.
To detect a slip of driving wheels is detected in such a traction control apparatus, it is necessary to control the engine output to a target engine output at which no slip occurs. For example, in a traction control apparatus having a main throttle valve controlled by an accelerator pedal and an electrically controlled sub throttle valve, provided in an intake path of an engine, an opening of the sub throttle valve must be controlled taking account of an opening of the main throttle valve to obtain a target engine output.